An opposed piston two stroke diesel engine may have high pressure (HP) exhaust gas recirculation (EGR) system and low pressure (LP) EGR system. The HP EGR system may transfer exhaust gases from upstream of a turbocharger turbine to a location downstream of a turbocharger compressor. Exhaust gas from the HP EGR system may also be directed into a supercharger compressor before it enters engine cylinders. The LP EGR system may transfer exhaust gas from downstream of an after treatment device and downstream of the turbocharger turbine to a location upstream of the turbocharger compressor. Exhaust gas from the LP EGR system may flow through the turbocharger compressor and the supercharger compressor. The LP EGR system may be activated when the HP EGR system is deactivated. Further, the HP EGR system may be activated when the LP EGR system is deactivated. However, there may be vehicle operating conditions where operating the HP EGR system or the LP EGR system may degrade engine performance over time.
The inventors herein have recognized that a LP EGR system may have advantages over a HP EGR system during some vehicle operating conditions and that the HP EGR system may have advantages over the LP EGR system during some vehicle operating conditions. As such, the inventors have developed a two stroke diesel engine operating method, comprising: receiving data indicative of a concentration of hydrocarbon (HC) and/or particulate matter (PM) emissions flowing from an engine to a controller; and deactivating a high pressure exhaust gas recirculation (EGR) system and activating a low pressure EGR system in response to the concentration of HC emissions and/or particulate matter (PM) flowing from the engine.
By activating and deactivating high and low pressure EGR systems responsive to a concentration of hydrocarbon emissions flowing from the engine, it may be possible to provide the technical result of providing EGR to an engine while reducing hydrocarbons and/or particulate matter that may create deposits on a compressor or foul the charge air cooler. In particular, the LP EGR system may be activated and the HP EGR system may be deactivated to reduce the possibility of hydrocarbons/particulate matter depositing on the compressor blades so that compressor balance and efficiency may be maintained as well as avoiding charge air cooler fouling/plugging. Hydrocarbons that exit the engine may be oxidized within an after treatment system so that EGR with a low concentration of hydrocarbons may be provided upstream of a supercharger compressor. Similarly, a diesel particulate filter (DPF) can remove PM exiting the engine to avoid fouling of the compressor and/or charge air cooler. In this way, exhaust gases may be scrubbed before entering the supercharger compressor during conditions when high concentrations of HC and/or PM may be present in engine exhaust gas.
The present description may provide several advantages. Specifically, the approach may allow a two stroke diesel engine to operate with EGR even when engine emissions comprising HC or particulate matter is higher than is desired. Further, the approach may decrease supercharger compressor and/or charge air cooler degradation. Further still, the approach may adjust EGR system operation responsive to whether or not the supercharger compressor is operating so that the activated EGR system conforms to other engine operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.